Technology update

Jun 26, 2008

Nanotubes on the look out for new bone

Multiwalled carbon nanotubes (MWCNTs) grown in pores on a titanium (Ti) surface are ideal for detecting bone growth, according to Thomas Webster and his team at Brown University, US. By adding the biosensing structure to the surface of orthopedic implants, the inventors hope to monitor the success of procedures such as hip replacements in situ.

Poor adhesion to the surrounding bone is the most common cause of hip replacement failure. Currently, the diagnosis of new bone growth can be problematic as today's imaging techniques each have their own limitations and difficulties – something that Webster and his colleagues hope to overcome.

"The idea is that our sensor will communicate the status of the surrounding tissue via radio frequencies to a handheld device," Webster told nanotechweb.org. "In fact, we've taken things a step further and coated our sensor with a drug-containing polymer layer that can be degraded to release bone building agents on demand."

The Ti-MWCNT biosensor works by measuring the conductivity of the tissue that forms on the implant. From this value, the scientists can determine whether the new material is bone, scar tissue or an infection. Calcium deposits associated with the formation of new bone cause the conductivity of the sensing surface to increase, unlike scar tissue and infection, which behave as resistors.

Setting up the surface
To prepare the sensor, the researchers begin by anodizing a 1 × 1 cm2 area of titanium. This creates a series of uniform nanopores that act as growing sites for a dense and entangled network of chemical vapour deposited MWCNTs.

It turns out that the MWCNTs play a dual role, both sensing and encouraging the growth of new bone around the implant.

Next, the team plans to begin animal studies. "It's a big and important jump to determine if the sensors will work in an animal," said Webster. "We'll be using rats and analyzing whether new bone growth can be measured and then controlled."

The bone sensing technology is currently being licensed by NanoVis, a start-up firm based in Indiana, US.